1. Field of the Invention
This invention relates to a glass intended to be used particularly as a panoramic roof for motor vehicles.
2. Description of the Prior Art
A panoramic roof lights the inside of a vehicle so equipped through the top, creating a less limited environment, closer to nature than the usual opaque roofs. To limit, particularly, the risks of glare and to improve the visual and thermal comfort of the passengers, a panoramic roof should be made of glass meeting certain conditions: Thus, light transmission through the glass should be limited, the light transmission factor preferably being less than 25%. Further, it is essential that the energy transmission also be limited, so as to avoid creating a greenhouse effect.
Herein energy transmission is understood to mean solar energy entering by direct transmission.
Various types of glass have already been proposed to be used as panoramic roofs, however, they fail to meet one or more of the required conditions.
A glass is known, for example, that is made of a sheet of glass tinted throughout and covered with a thin semireflective layer. A light transmission factor on the order of 25% and an energy transmission factor (ETF) on the order of 30% can be obtained by using this glass. However, it is impossible to attain still lower light and energy transmission factors, of a value on the order of 10 to 15% which are desirable to increase the feeling of comfort. Although, by increasing the thickness of the semireflective layer, particularly beyond about 80 nanometers, these low coefficient values can in fact be attained such a thickness results in marked iridescence and unacceptably high interference.
A glass is also known that is made up of a sheet of clear glass covered with a network of enamel points which, theoretically, make it possible to lower the light transmission factor as much as desired by increasing the surface covered by these points, but in practice, since the energy transmission factor in such a glass is always greater than the light transmission factor, it remains impossible to lower the overall energy transmission factor to values less than 25%, while retaining sufficient lighting.
Automobile manufacturers are increasingly demanding in regard to the qualities of glasses intended for vehicles, particularly as panoramic roofs, and the characteristics of known glasses do not meet these demands.
Another obstacle encountered is that infrared radiation can cause eye fatigue and, for this reason, efforts have been made to develop glasses for which the energy transmission factor is preferably less than the light transmission factor, or at least for which the two factors are very close to one another, while being low enough to maintain a feeling of comfort.
This invention provides a new glass structure that overcomes these prior art problems and makes available glass suitable for application as a panoramic roof for motor vehicles, satisfying an increasing need in the industry.